Spark plug



April 8, 1952 E. R. PAUL 2,591,718

SPARK PLUG Filed Jan. 16, 1950 QD'MILPaIu/L Patented Apr. 8, 1952 UNITED STATES PATENT QFFKCE SPARK PLUG Edwin R. Paul; Washington, D. 0. Application anuary '16, 1950, Serial No. 138,874

t ara-fins (01. 123-469) (Granted; under thejact or March a, 1883,; as

The present invention relates to a: spark plug andmore particularly to a spark. plug; of the multiple gap type and a method of making. the same.-

An-object' of the present invention: is the provisionof a-muItiple gap spark plug whichexhibits superior anti-fouling and slower erosion rate characteristics.

Another object isto provide a. spark plug having means for keepingthe insulated electrodeand-theinsulator free of objectionable deposits of oil and combustion products thereby prevent i'ngfouling and preignition.

A-further object of this invention isito provide a spark plug having a plurality" of apertures between the grounded electrodes to provide ready and thoroughscavenging of the central electrode and the insulator.

Still another object is to provide a multiple gap spark plug having a plurality" of I semi-sur face spark gaps without restricting. thorough scavenging of "the insulation.

Fig. 3 is a sectional view of the plug taken along the line 33 of Fig. 2, looking in the direction of the arrows; and.

Fig. 4 is a section taken along the line 4-4 of Fig. 1, looking in the direction of the arrows.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. 1 a conventional spark plug having a metallic body or shell, generally designated H, the lower end of shell ll being externally threaded, as shown at l2, so that the plug may be readily inserted in the engine block. Coupled to shell II in a conventional manner, as shown in Fig. 3, is an insulating body l3, preferably made of porcelain, there being a v central electrode l4 extending axially through insulating body I3.

In carrying out the present invention, several amended April at, 1928;. 3'70 G. 757) rounds of threads are preferably turned off of the lower end of threaded portion l2 of shell II, and a multiplicity of slots [5 are cut in the turned end of shell ll, leaving a multiplicity of projections [6, preferably four in number, ex-

tending longitudinally from shell H, as shown in Fig. 1.

Projections 16 are preferably of the form shown in Figs. 2 and 4 having a relatively large substantially rectangular upper base portion and a relatively small substantially rectangular lower base portion, the transition between lower and upper portions being substantially linear except forrthe curvature ll adjacent the upper portion. Projections i6 are constructed in this manner in order to insure a smooth temperature gradient between the upper and lower portions to thereby insure a smaller concentration of heat. In this manner, there is eliminated any possibility of deformation of the threaded portion I-Zat the major diameter with a resultant seizing of the plug in the cylinder. To each projection I6 is secured an electrode l8which projects radially towards the axis of shell H, opposite electrodes being diametrically aligned; as" shown in Figs. Za'nd 3. Electrodes l8 are preferably secured to projections It by means'of spot welding in order'to eliminate the introductionof 'a'notherme'tal with its subsequent pitting; 1

m maung body [3 and central electrode M are preferablyground off so that'upon assembly body" [3 just touches all of electrodes l8, electrodesm'terrriinating short of electrode M, to form amultiplicity of semi-surface spark gaps, as shown in Figs. 2 and 3. By this arrangement, the spark discharges occur across the end sur- "faces of body l3 and electrode l4 thereby exposing these surfaces to higher temperatures to keep them free of objectionable deposits of oil or combustion products, which would otherwise cause fouling and lead to preignition.

In addition, slots I5 in the turned end of shell ll form apertures for permitting a fresh charge to sweep the gap between electrode it and electrodes'l 8 to thereby cool the end surfaces of body l3 and electrode 14. In this manner, the gap is always surrounded with a fresh charge, and thorough scavenging of the end surfaces of body 13 and electrode M is attained. Finally, slots [5 permit freedom of movement of the exhaust gases, as shown in Fig. 4, thus avoiding the deleterious efiects of trapped gases in the region surrounding electrode I4.

Obviously, many modifications and variations 3 of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

The invention described herein may be manufactured and used by or for the Govermnent of the United States of America for govenmental purposes without the payment of any royalties thereon or therefor.

What is claimed is:

1. A spark plug comprising a shell, a central electrode disposed axially of said shell and extending beyond the lower end thereof, an insulating body surrounding said electrode and having its lower end surface coplanar with the lower end surface of said electrode, a plurality of spaced longitudinal projections on the end of said shell, and an electrode mounted on each of said projections and extending radially towards said central electrode, the inner end of each of the radially extending electrodes resting upon the lower end surface of said insulating body,

2. A spark plug according to claim 1, each of said radially extending electrodes terminating short of said central electrode to form spark gaps.

3. A spark plug according to claim 1, wherein each of said projections is tapered downwardly, said radially extending electrode being mounted on the lower end of said projection.

4. A spark plug comprising a shell, a central electrode positioned axially of said shell and extending beyond the lower end thereof, an insulating body surrounding said electrode and having its lower end surface coplanar with that of said electrode, a plurality of spaced integral projections extending longitudinally of said shell, and an electrode mounted on each of said projections and extending radially toward said central electrode, the inner end of each radially extending electrode resting upon the lower end of said insulating body to form a semi-surface spark gap between said central electrode and said radially extending electrode.

5. The method of constructing a spark plug having a central electrode surrounded by an insulator and a shell, said method comprising cutting a plurality of slots in the lower end of the shell to form spaced projections thereon around the lower end of said insulator, mounting an electrode on each of said projections to extend radially towards the central electrode, grinding 4 the end of said central electrode flush with the end of said insulator, and aligning the lower end surfaces of said insulator with the upper surface of each radially extending electrode to bring them in ,contact.

6. The method of constructing a spark plug having a central electrode surrounded by an insulator and an outer shell which comprises cutting a plurality of apertures in the lower end of the shell to form spaced projections thereon around the lower end of said insulator, mounting an electrode on each of said projections to 'extend radially towards the central electrode,

grinding off the lower ends of the central electrode and the insulator to the point where the remaining lower end surfaces of the central electrode and the insulator are contiguous, and aligning said surface of the insulator with the upper surface of the end of each radially extending electrode for full contact therebetween.

7. The method of constructing a multi-gap spark plug having a threaded shell and a central electrode surrounded by an insulator which comprises turning off several rounds of threads at the lower end of the shell, cutting a plurality of apertures in the de-threaded end of the shell to form spaced projections thereon around the lower end of said insulator, mounting an electrode on each said projections to extend radially toward the central electrode, grinding the end of said central electrode flush'with the end of said insulator, and aligning the lower end surface of the insulatorwith the upper surface of each radially extending electrode to provide contact therebetween.

EDWIN R. PAUL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain IMay I5, 1941 

